For example, if an administration official once worked as a lobbyist, an ethics waiver could allow that person to bypass the rules that are meant to prevent them from working on matters related to their lobbying.

Last week, Mick Mulvaney, the director of the Office of Management and Budget, asked ethics office director Walter Shaubto stop the inquiry, and questioned his authority to ask for the names of anyone granted an exemption.

If the budget office "does not stand down," the Senators wrote in their letter, "we will seek the waivers directly ourselves."

"The Administration cannot dispute that Congress has the right to this information," they wrote.

The letter from lawmakers also mentioned Trump's executive order from January, which prohibits former lobbyists from participating in anything directly related to the businesses of former employers or clients for two years.

Lawmakers said Shaub's request is "necessary for assuring Americans that the Trump administration is taking its own ethics pledge seriously."

Mulvaney's office did not immediately respond to a request for comment Tuesday.

Before Shaub's letter was made public Monday night, the budget office said in a statement that it "stands firmly in support of the highest ethical standards." But it said the request for the waivers had an "expansive scope and breathless timetable."